The present invention relates to a moisture sensitive element and a method of manufacturing the same and, more particularly, to a capacitive moisture sensitive element having a moisture sensitive film consisting of an organic polymer resin and a method of manufacturing the same.
In conventional moisture sensitive elements of this type, an organic polymer such as cellulose acetate butyrate, cellulose acetate propionate, polyimide, or linear polyamide obtained by polymerizing a linear high-molecular weight polyamic acid is used as a moisture sensitive material. Japanese Patent Laid-Open No. 62-88951, for example, discloses a moisture sensitive element utilizing a change in capacitance of a moisture sensitive film consisting of the above moisture sensitive material to detect a humidity.
A moisture sensitive element having the above structure, however, is highly hydrophilic (i.e., the nature having an affinity for absorbing water), i.e., has a high water absorbing rate. A large amount of water strongly bonded to a polymer by chemical or physical adsorption is left in the moisture sensitive element. For this reason, when a moisture sensitive element is used for a long period of time at a high temperature (e.g., about 40.degree. C.) and a high humidity (e.g., about 90%), long-term stability is undesirably degraded, which results in drifting its output value. A difference (hysteresis) in moisture sensitive characteristics between the humidification and dehumidification processes is small at room temperatures, but is large at low temperatures, thus prolonging the response time. In addition, when a moisture sensitive element is used at a low humidity for a long period of time, the hysteresis is undesirably increased. Output values drift due to the occurrence of moisture condensation and water immersion. When a moisture sensitive element is exposed in an organic solvent, its output value drifts. When a moisture sensitive element has temperature dependent characteristics, they must be corrected with a heat-sensitive element (i.e., a temperature sensor).